Citrus micrantha
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The micrantha is a wild
citrus ''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is native to ...
from the papeda group, native to southern
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
, particularly islands of
Cebu Cebu (; ceb, Sugbo), officially the Province of Cebu ( ceb, Lalawigan sa Sugbo; tl, Lalawigan ng Cebu; hil, Kapuroan sang Sugbo), is a province of the Philippines located in the Central Visayas region, and consists of a main island and 16 ...
and
Bohol Bohol (), officially the Province of Bohol ( ceb, Lalawigan sa Bohol; tl, Lalawigan ng Bohol), is an island province of the Philippines located in the Central Visayas region, consisting of the island itself and 75 minor surrounding islands. ...
. Two
varieties Variety may refer to: Arts and entertainment Entertainment formats * Variety (radio) * Variety show, in theater and television Films * ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont * ''Variety'' (1935 film), ...
are recognized: small-flowered papeda (''C. hystrix'' var. ''micrantha''), locally known as ''biasong'', and small-fruited papeda (''C. hystrix'' var. ''microcarpa'') or ''samuyao''. Long viewed as a separate species, ''C. micrantha'', it is now generally viewed to fall within ''
Citrus hystrix ''Citrus hystrix'', called the kaffir lime or makrut lime, (, ) is a citrus fruit native to tropical Southeast Asia. Its fruit and leaves are used in Southeast Asian cuisine, and its essential oil is used in perfumery. Its rind and crushed leav ...
'', but genomic data on the latter is insufficient for a definitive conclusion. A micrantha was one of the
progenitor In genealogy, the progenitor (rarer: primogenitor; german: Stammvater or ''Ahnherr'') is the – sometimes legendary – founder of a family, line of descent, clan or tribe, noble house, or ethnic group.. Ebenda''Ahnherr:''"Stammvater eines ...
species of some varieties of lime.


Description

The micrantha was first described to Western science in 1915 by
Peter Jansen Wester Peter Jansen Wester (23 September 1877 – 1931; occasionally referred to himself as Peter Johnson Wester) was a Swedish-American agricultural botanist. Born in Sweden, he emigrated to the United States in 1897. Wester worked in several agricultura ...
, who worked for the Philippine Bureau of Agriculture at the time.


Biasong

Wester collected ripe fruit specimens of biasong (small-flowered papeda, ''Citrus hystrix'' var. ''micrantha'') on islands of Cebu, Bohol,
Dumaguete Dumaguete, officially the City of Dumaguete ( ceb, Dakbayan sa Dumaguete; fil, Lungsod ng Dumaguete), is a 3rd income class component city and the capital of the province of Negros Oriental, Philippines. According to the 2020 census, it has a p ...
,
Negros Negros is the fourth largest and third most populous island in the Philippines, with a total land area of . Negros is one of the many islands of the Visayas, in the central part of the country. The predominant inhabitants of the island region a ...
, and in the Zamboanga and Misamis provinces in
Mindanao Mindanao ( ) ( Jawi: مينداناو) is the second-largest island in the Philippines, after Luzon, and seventh-most populous island in the world. Located in the southern region of the archipelago, the island is part of an island group of ...
. The fruits were collected throughout the year, indicating that the plant is ever-bearing. Biasong is characterized by small flowers (thus the "small-flowered" moniker) with fewer
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the fila ...
s than other papedas and oblong-obovate, few-
locule A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...
d fruits. Inhabitants did not use the fruits for food, but for hair-washing, and it had little economic importance. Biasong's aroma is similar to that of the samuyao variety of micrantha. The tree reaches in height. Leaves are long, wide, broadly elliptical to
ovate Ovate may refer to: * Ovate (egg-shaped) leaves, tepals, or other botanical parts *Ovate, a type of prehistoric stone hand axe *Ovates, one of three ranks of membership in the Welsh Gorsedd *Vates In modern English, the nouns vates () and ova ...
,
crenate A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
, thin, with base rounded or broadly acute; apex acutely blunt pointed. Petioles are long, broadly winged, up to wide, with wings (phyllodes) sometimes larger than the leaf. Flowers are small, four-petaled, white with a thin purple edge, in diameter, forming
cymes An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed ...
of two to five. There are 15 to 17 equal
stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the fila ...
s. The ovary is obovoid, with 6 to 8 slender, distinct
locule A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...
s. Fruits are
obovate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular ...
to oblong-obovate, long, with diameter of , averaging in weight; their skin is rather thick, lemon-yellow, fairly smooth or with transverse corrugations; the pulp is juicy, grayish and acid, while juice cells are short and blunt to long, long, slender and pointed, sometimes containing a minute, greenish nucleus. They have numerous flat, pointed,
reticulate Reticulation is a net-like pattern, arrangement, or structure. Reticulation or Reticulated may refer to: * Reticulation (single-access key), a structure of an identification tree, where there are several possible routes to a correct identificati ...
seeds.


Samuyao

Wester collected ripe samuyao (small-fruited papeda, ''Citrus hystrix'' var. ''microcarpa'') fruit specimens from cultivation in Cebu and Bohol in June, and from November to February. Samuyao is rather smaller than biasong, with trees attaining 4.5 meters. It has small, thin leaves and flowers comparable in size to biasong. The fruit, 15–20 mm in diameter, is likely to be the smallest in the whole genus. Wester also recorded a somewhat more vigorous variety, called "samuyao-sa-amoo" in Bohol, with slightly larger fruits; there is a possibility that this species was actually ''Limonellus aurarius'', described by Georg Eberhard Rumphius back in 1741 in a nearby area, although his description also fits a number of related species. Wester gave the botanical description: Clear, intensely fragrant oil can be produced from the samuyao peel, and it has been used as a hair fragrance by women who live where it grows.


Toxicity

The micrantha contains a significant amount of
bergapten Bergapten (5-methoxypsoralen) is a naturally-occurring organic chemical compound produced by numerous plant species, especially from the carrot family Apiaceae and the citrus family Rutaceae. For example, bergapten has been extracted from 24  ...
, a linear
furanocoumarin The furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. Most of the plant species found to contain furanocoumarins belong to a handful of plant families. The families Apiaceae and Rutace ...
well known for its phototoxic effects. Of 61 ''Citrus'' varieties tested, ''C. micrantha'' had the highest concentration of bergapten of any ''Citrus'' species. In particular, ''C. micrantha'' contained almost twice as much bergapten as the
bergamot orange ''Citrus bergamia'', the bergamot orange (pronounced ), is a fragrant citrus fruit the size of an orange, with a yellow or green color similar to a lime, depending on ripeness. Genetic research into the ancestral origins of extant citrus cult ...
whose essential oil is highly phototoxic. Indiscriminate use of bergamot essential oil has led to several cases of
phytophotodermatitis Phytophotodermatitis, also known as berloque dermatitis or margarita photodermatitis, is a cutaneous phototoxic inflammatory reaction resulting from contact with a light-sensitizing botanical agent followed by exposure to ultraviolet light (from ...
, Cited i
CIR 2013
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a potentially severe skin inflammation. In these cases, the primary causal agent is believed to be bergapten.


Hybrids

The Key lime (''Citrus aurantifolia'') is a hybrid of the micrantha and the citron. It, in turn, has been crossed with a lemon to produce the
Persian lime Persian lime (''Citrus'' × ''latifolia''), also known by other common names such as seedless lime, Bearss lime and Tahiti lime, is a citrus fruit species of hybrid origin, known only in cultivation. The Persian lime is a triploid cross between ...
(''C. latifolia''). There are lumias that are distinct micrantha/citron hybrids, such as the Pomme d'Adam, while other lumias, like the Borneo lemons, are micrantha/citron/pomelo tri-species hybrids. An Indonesian hybrid, the nansaran (''C. amblycarpa''), is a ''C. hystrix''/''C. reticulata'' cross.


References


External links


Searching for the Elusive Samuyao
"Our Philippine Trees" blog

"Our Philippine Trees" blog {{Taxonbar, from=Q20704151 Micrantha Flora of the Philippines Plants described in 1915